The present invention relates generally to a rotation rate measuring instrument, and more particularly to an instrument of this type in which light beams launched into a looped optical fiber in opposite directions are evaluated to obtain the rotation rate therefrom.
An instrument of this kind is disclosed in German Pat. No. 31 36 688. In this instrument, a light beam generated in a light source is split into two beam portions which travel in opposite directions through an optical fiber arranged to enclose an area at least once. At least one of the two beam portions is modulated before entering the optical fiber and the two beam portions emerging from the optical fiber are combined, the combined light beam so produced being directed onto a photodetector, from the output signal of which the rotation rate is derived. In such a device, the signal to be evaluated depends on, inter alia, the intensity (I.sub.O) of the light emitted by the light source and on the attenuation (.alpha.) of the light propagating in the light paths. Variations of these quantities are disadvantageous during evaluation.
German published application DE-OS No. 30 40 514 discloses a rotation rate measuring instrument of the same kind. One of the solutions described there is to split the output signal of the photodetector into at least two signal components of different frequencies. A control signal is derived from one of the signal components. The control signal is used to control a phase modulator which modulates the light traversing a coiled optical fiber. The control is such that at least one of the signal components becomes as small as possible.